MRO — Maintenance, Repair and Overhaul

MRO — Maintenance, Repair and Overhaul

MRO is a major industry in its own right. The global aviation MRO market is valued at over $80 billion annually and encompasses airlines' own maintenance divisions, independent MRO providers and original equipment manufacturer (OEM) service networks.

MRO Categories

Aircraft maintenance is broadly divided into: Line Maintenance — routine checks performed between flights and overnight, keeping the aircraft in service; Base Maintenance — scheduled heavy checks (C Check, D Check) performed in a hangar with the aircraft out of service for days or weeks; Engine Overhaul — removal and complete rebuild of powerplants; Component Overhaul — repair and certification of individual components (avionics, landing gear, APU).

Regulatory Framework

All MRO activity is governed by airworthiness regulations. In Europe, EASA Part-145 certifies maintenance organisations. In the US, FAA Part 145 covers repair stations. Airlines must use approved maintenance organisations and follow the Aircraft Maintenance Programme (AMP) derived from the manufacturer's Maintenance Review Board (MRB) document.

The Maintenance Programme

Each aircraft type has a manufacturer-defined maintenance programme specifying what must be checked, how often and to what standard. Airlines work with regulators to develop their own AMP based on this document. The intervals are defined in flight hours, flight cycles or calendar time — whichever is reached first.

MRO and Aircraft Economics

Maintenance costs represent approximately 10–15% of an airline's total operating costs. The balance between in-house MRO capability and outsourcing to third-party providers is a strategic decision driven by fleet size, aircraft type and cost structure.